1. Field of the Invention
The present invention relates to a picture system, and more particularly, to a method for encoding and decoding a picture signal for detecting and correcting errors in a new structured GOB according to a data partition technique.
2. Background of the Related Art
In general, if a signal to be transmitted or stored is represented with a series of different symbols, coding is representation of each of the symbols with a length of code, wherein representation of each symbol with the same lengths of codes is called as a fixed length coding, and representation of each symbol with different lengths of codes is called as a VLC (Variable Length Coding). In the VLC in which respective symbols are represented with different lengths of codes, codes with short lengths are assigned to the symbols with a high frequency of occurrence in view of probability, and codes with relatively long lengths are assigned to the symbols with a low frequency of occurrence in view of probability, resulting to represent the signal with a less number of bits compared to the fixed length coding in which the same lengthed symbols are assigned to all symbols. However, though the VLC is efficient in compressing an amount of information, the VLC has the following disadvantages compared to the fixed length coding in an environment channel errors are occurred, frequently. That is, in the case of the fixed length coding, when the codes representing a symbol is contaminated by a channel error, only the symbol is affected. However, in the case of VLC, as the codes for each symbol has a proper length, if a channel error is occurred at a symbol coded to a particular length, not only the contaminated symbol, but also following successive symbols are affected because the codes contaminated by the error can be mistaken as codes for other symbol, i.e., even synchronization information for each code can be lost. In conclusion, when information is compressed by the VLC in transmission of information in an environment of high channel error occurrence, a method for supplementing the disadvantage is required. One of the most general supplementing method is to provide a system as shown in FIG. 1. FIG. 1 illustrates a block diagram showing a system provided for supplementing the disadvantage of the related art VLC.
Referring to FIG. 1, on the transmitter side, a channel encoding part 3 is connected to a rear end of a source coding which contains variable length coding part 2. And, on the receiver side, a source decoding block 5 is connected to a rear end of a channel decoding part 4. The channel encoding part 3 adds a redundancy to a picture received through a camera before coding the picture, so that the channel decoding part 4 on the receiver side can detect occurred error and restore an original picture even if there is a channel error occurred. Though this is for enhancing a resilience to the error occurrence, since the redundancy is added without information on a GOB (Group Of Block) to be subjected to VLC, this may deteriorate a compression efficiency, significantly. To cope with this problem, other techniques for removing the error are employed recently, having a higher resilience for the channel error occurrence. One of the representative algorithms is the coding technique recommended by H.263 of ITU-T, another is the coding technique recommended by the MPEG-4 in the IEC (International Electrotechnical Commission) of the ISO (International Organization for Standardization). The techniques are the resynchronization, the data partitioning, the reversible variable length codes, which can provide an error compensation of approx. 2˜3 dB, presently. The data partitioning is one of technique for enhancing resilience to the channel error occurrence, together with the channel coding.
The channel coding and the data partitioning will be explained in more detail. In the channel coding, the Reed-Solomon code, the BCH code (Bose-Chaudhuri-Hocquenghem code), or the convolution code are used as one of error correction code. The channel coding by using the BCH code is one of block coding method for detection of random errors and error correction of independent various bits. The block coding method is a coding method in which information bits to be transmitted is partitioned into fixed sizes of blocks, and parity bits, error detection bits, are added to each of the blocks. However, the channel coding by using the Reed-Solomon code is one of block coding for burst error detection and correction. What the two block coding methods of the channel coding have in common is the partition into fixed sizes of blocks and addition of redundancy bits thereto for protection of the blocks. In this instance, the blocks are partitioned without considering information on the codes of the blocks, at all.
The data partition technique will be explained. For reference, in the case of moving picture compression recommended by the MPEG-4, the VLC picture is partitioned in GOBs. The GOB includes headers, moving vectors, and discrete cosine transform coefficients. FIG. 2 illustrates a GOB partition structure according to the related art data partition technique.
Referring to FIG. 2, in the related art data partition, a data is partitioned into three GOB regions 11, 13 and 15 of headers, moving vectors, and discrete cosine transform coefficients. The three regions 11, 13 and 15 are regions of the header, the moving vector, and the discrete cosine transform coefficient of each of 8 macro blocks in the GOB. There are partition markers 12 and 14 provided between the three regions 11, 13, and 15 for making the three regions 11, 13, and 15 distinctive. And, there is a resynchronization marker 10 added to a front of the GOB, so that the source decoding part in FIG. 1 can detect a starting point of the next GOB when damage to a portion of the GOB by an error is detected. The contents of the GOB is partitioned into the three regions because, though restoration of the picture is very difficult if the header region 11 is damaged by the error, a close restoration of an original picture is possible comparatively by using information in the header region 11 when only the moving vector region 13 is damaged, and a very close restoration of an original picture is possible by using information in the header region 11 and the moving vector region 13 when only the discrete cosine transform coefficient region 15 is damaged. If the contents of the GOB is not partitioned thus, even if the discrete cosine transform coefficient region 15 is damaged, since the receiver side can not know whether the discrete cosine transform coefficient region 15 is damaged, or the header region 111 or the moving vector region 13 is damaged, a result that the entire GOB is damaged is brought about.
However, the related art channel coding and data partition have the following problems.
First, even if the GOB is partitioned into different information regions, the related art data partition has no method for protecting the partitioned regions individually, and, when the partition marker used for making the respective regions distinctive is damaged by the error, affect of the damage will be great. Nevertheless, it has been difficult to add any device for protecting the damage to the partition marker as a method for solving the problem.
Second, the provision of redundancy regardless of the contents of the variable length coded GOB in the related art channel coding for enhancing resilience to the error occurrence drops a compression efficiency, significantly.